The present invention relates to methods and devices for contraception which depend upon spermicidal activity of 1-substituted imidazoles applicable to the female mammal intravaginally. More specifically, the present invention concerns intravaginal inserts, such as diaphragms, rings, or cervical caps which contain, within the matrix of the material of which they are composed, a spermicide of the chemical class of 1-substituted imidazoles and a pharmaceutically acceptable chelating agent, and which devices are capable of releasing an effective amount of said spermicide at a controlled rate in situ.
Present methods of contraception suffer from a variety of well known defects. Systemically active drugs which alter the ovulatory cycle of the female, whether taken orally, or inserted in the uterus or vagina for slow release, cause a substantial number of side effects ranging from discomfort and menstrual irregularities to life threatening alterations in metabolism. Mechanical barriers, such as condoms and diaphragms, in their present form, are not ideally effective, and, more importantly, do not have maximum user acceptance because of the necessity of their being employed in the same psychological time frame as intercourse. Spermicidal preparations designed for intravaginal application are even less effective and less aesthetically acceptable than the aforesaid mechanical barrier devices. The goal of a contraceptive which is (a) effective (b) confined in its metabolic effects to contraception itself, and (c) can be employed at a time far psychologically removed from the sex act, has not been achieved in the prior art.
Intravaginal devices for release of contraceptive materials are well known, and many designs have been described: for example, a vaginal contraceptive tampon is described in international application published under No. PCT 80/00008 (claiming priority from U.S. application Ser. No. 888,578); a vaginal medicator in U.S. Pat. No. 3,885,564; a vaginal ring in U.S. Pat. No. 3,545,439; a diaphragm in U.S. Pat. No. 2,087,610, and a cervical cap in U.S. Pat. No. 2,836,177.
Devices for the release of a progestational agent as the active ingredient have also been described: (WHO Special Programme of Research, Development and Research Training in Human Reproduction, Geneva, Switzerland: Journal of Steroid Biochemistry 11 (1B) 461 (1979); Burton, F. G., et al, Contraception 17 (3) 221 (1978); Gordon, N. R., et al, Saf. Health Plast. Nat'l. Tech. Conf. Soc. Plast Engr. 1977, 109. Victor, A., et al, Contraception, 16 (2) 125 (1977), Zanartu, et al, Steroids 21 (3) 325 (1973); British patent application No. 2,616,064. However, the results have been unsatisfactory because of continuing problems with unwanted metabolic alterations and because of the difficulty of assuring proper release of the steroid (WHO study, supra). As systemic contraceptives, progestational compounds are subject to causing such side effects regardless of the mode of administration.
Release of spermicides, because the effect is not systemic to the female host, is an inherently more desirable option. Devices which release spermicides of the surfactant type have also been described: Stone, et al, Am. J. Obstet. and Gynecol. 133 (6): 635 (1979), U.S. Pat. No. 4,031,202, British Pat. No. 1,329,619, European Pat. Nos. 9-417 and 9-518. However, surfactant spermicides are effective only at relatively high concentrations, and devices which remain in the vaginal cavity are incapable of releasing effective amounts over long periods. Furthermore, surfactants are not effective within the cervical mucus. Hence, effectiveness is impaired because the critical sperm pathway through the mucus to effect conception remains unimpaired.
The present invention utilizes 1-substituted imidazole spermicides and a pharmaceutically acceptable chelating agent. Because of the effectiveness of these spermicides at low concentrations, intravaginal devices which incorporate them and a pharmaceutically acceptable chelating agent into the matrix of the device are capable of releasing effective quantities for a prolonged period to be absorbed by the cervical mucus. The devices and method of this invention thus permit a method of contraception which is esthetically more appealing and provides greater protection than the above known methods.